\begin{tabular}{cccc}
	A     & B                         & C     & D \\
	AAA   & BBB                       & CCC   & DDD \\
	\multicolumn{2}{c}{first heading} & \multicolumn{2}{c}{second heading} \\
	one   & two                       & three & four \\
	five  &                           & six   & \\
	seven & \\
\end{tabular}
